Comparative study of partial volume correction methods in small animal positron emission tomography (PET) of the rat brain

Quantitative accuracy in rat brain PET studies is reduced by partial volume effect. We investigated the performance of partial volume correction (PVC) in a realistic situation where activity is also taken up in the head and spills into the brain. The PVC approaches studied include the region-based geometric transfer matrix (GTM) method and voxel-based iterative deconvolution (reblurred Van Cittert and Richardson-Lucy). 8 realizations of dynamic rat brain PET studies of
¹¹
C-Raclopride with a binding potential BP
_ND
=3 in the striatum were simulated with the Monte Carlo simulator PET SORTEO. Synthetic time activity curves (TACs) were assigned to the striatum, cerebellum, remaining brain and head regions outside the brain of a rat head phantom. Different sized volumes of interest (VOIs) were sampled ranging from the full anatomical region to smaller VOIs containing only voxels with at least 50%, 70% or 90% of the maximum activity. BP
_ND
was calculated for the striatum using the simplified reference tissue model with the cerebellum as the reference tissue. Without PVC the accuracy of BP
_ND
was very low for all VOI sizes with biases between -44.7% and -20.9%. PVC using the GTM method was only accurate for the smallest 90% VOI with a bias of -7.7% but the standard deviation increased to 4.2% compared to less than 1% for the larger VOIs. Good accuracy was achieved for both iterative deconvolution methods using the 50% VOI (bias less than 8%) with standard deviations of less than 1.8%. Thus, in the presence of activity uptake outside the brain, iterative deconvolution methods outperform the GTM method. We are currently implementing PVC with a spatially variant PSF to better compensate for non-uniformities of spatial resolution away from the centre of the field of view.